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A man shot and killed his estranged wife's boyfriend Wednesday night before attempting to take his own life, say Anne Arundel County Police. (Published Thursday, Aug. 21, 2014)

A man shot and killed his estranged wife's boyfriend Wednesday night before attempting to take his own life, say Anne Arundel County Police.

Kathy Mendiola said that she and her boyfriend, Howard Richard Popp Jr., were sitting in his car when her estranged husband showed up at her home in the 3300 block of Sudlersville South in Laurel around 10:40 p.m. Wednesday.

Estranged Husband Kills Wife's Boyfriend, Shoots Self: PD

Anne Arundel County police say a man fatally shot his estranged wife's boyfriend before attempting to take his own life. (Published Thursday, Aug. 21, 2014)

She told News4's Megan McGrath that Popp, 39, got out of the car to talk, and that's when her estranged husband pulled out a gun.

"They were talking, so I got in between them to try and stop it. My ex-husband pulled out the gun; he stepped back and shot him," Mendiola said.

Authorities say Robert Babauta Mendiola, 39, shot Popp multiple times and then ran from the scene. They arrived to find Popp, a Baltimore resident, lying in the roadway.

Officers and paramedics attempted CPR although authorities said there was no visible signs of life. Popp was pronounced dead at a hospital.

Officers searched the area for the suspect and found that he had barricaded himself in a shed in the 300 block of Old Line Avenue. Members of the Special Operations Section were able to get into the shed and found the suspect suffering from what appeared to be a self-inflicted gunshot wound.

Robert Mendiola, of Laurel, was taken to the University of Maryland Shock Trauma Hospital with life-threatening injuries and is currently under guard there.

He has been charged with first- and second-degree murder, among other charges.

Investigators say the Mendiolas had separated from her husband last month, and Kathy Mendiola had obtained a Final Protective Order against him, which was in effect until next year. Her husband had been trying to reconcile with her, but she had started dating Popp, authorities said.

"I was in an abusive marriage for 20 years, and I finally had the guts to leave," Kahty Mendiola said. "I met Howard. Ever since I met him I was happy; I was alive again."

Crying on her front porch, Kathy had a message for Popp's family.

"If they see this, I'm so sorry. I didn't mean for any of this to happen."

This was Anne Arundel County's third domestic-related homicide of the year, authorities said.

Stay with NBCWashington on-air and online for more on this developing story.